This invention relates to operator carried power tools and more particularly, to operator carried power tools driven by a small internal combustion engine.
Portable operator carried power tools such as line trimmers, blower/vacuums, or chain saws are currently powered by two-cycle internal combustion engines or electric motors. With the growing concern regarding air pollution, there is increasing pressure to reduce the emissions of portable power equipment. Electric motors unfortunately have limited applications due to power availability for corded products and battery life for cordless devices. In instances where weigh is not an overriding factor such as lawn mowers, emissions can be dramatically reduced by utilizing heavier four-cycle engines. When it comes to operator carried power tools such as line trimmers, chain saws and blower/vacuums, four-cycle engines pose a very difficult problem. Four-cycle engines tend to be too heavy for a given horsepower output and lubrication becomes a very serious problem since operator carried power tools must be able to run in a very wide range of orientations.
The California Resource Board (CARB) in 1990 began to discuss with the industry, particularly the Portable Power Equipment Manufacturer""s Association (PPEMA), the need to reduce emissions. In responding to the CARB initiative, the PPEMA conducted a study to evaluate the magnitude of emissions generated by two-cycle engines in an effort to determine whether they were capable of meeting the proposed preliminary CARB standards tentatively scheduled to go into effect in 1994. The PPEMA study concluded that at the present time, there was no alternative power source to replace the versatile lightweight two-stroke engine currently used in hand held products. Four-cycle engines could only be used in limited situations, such as in portable wheeled products like lawn mowers or generators, where the weight of the engine did not have to be borne by the operator.
It is an object of the present invention to provide a hand held powered tool which is powered by an internal combustion engine having low emissions and is sufficiently light to be carried by an operator.
It is a further object of the present invention to provide a portable hand held powered tool powered by a small internal combustion engine having an internal lubrication system enabling the engine to be run at a wide variety of orientations typically encountered during normal operation.
It is a further object of the present invention to provide a portable power tool to be carried by an operator which is driven by a small lightweight four-cycle engine having an aluminum engine block, an overhead valve train and a splasher lubrication system for generating an oil mist to lubricate the crank case throughout the normal range of operating positions.
It is yet a further object of the invention to provide an oil mist pumping system to pump an oil mist generated in the crank case into the overhead valve chamber.
These objects and other features and advantages of the present invention will be apparent upon further review of the remainder of the specification and the drawings.
Accordingly, a portable hand held power tool of the present invention intended to be carried by an operator is provided utilizing a small four-cycle internal combustion engine as a power source. The four-cycle engine is mounted on a frame to be carried by an operator during normal use. The tool has an implement cooperating with the frame having a rotary driven input member coupled to the crankshaft of the four-cycle engine. The four-cycle engine is provided with a lightweight aluminum engine block having at least one cylindrical bore oriented in a normally upright orientation having an enclosed oil reservoir located therebelow. A crankshaft is pivotably mounted within the engine block. The enclosed oil reservoir when properly filled, enables the engine to rotate at least 30 degrees about the crankshaft axis in either direction without oil within the reservoir rising above the level of the crankshaft counter weight. A splasher is provided to intermittently engage the oil within the oil reservoir to generate a mist to lubricate the engine crank case.
One embodiment of the invention pumps an oil mist from the crank case to an overhead valve chamber to lubricate the valve train.
In yet another embodiment of the invention, the overhead valve chamber is sealed and is provided with a lubrication system independent of the crank case splasher system.